Revision as of 00:21, 10 August 2012

Contents

Overview

Digital Speech decoder is an open source software package that decodes several
digital speech formats. It uses the mbelib library (a separate open source package)
to synthesize the decoded digital speech. It does not allow decoding of encrypted
communications. It can save the compressed digital audio bits to "mbe" data files
(.imb and .amb extensions) and play back those saved files. It's discussed in this forum

The latest version 1.4 supports the following formats and modulation types:

OpenSky - four slot format vocoder may be supported by mbelib. Will not be supportable if it is determined that voice encryption is not optional

D-STAR - Voice frames recognized, vocoder not supported by mbelib. May be possible to pass voice bits to DVDongle.

Other formats will only be considered if high quality samples of the signals are made available for download by the developers. Samples must be from a discriminator tap, .wav format, 48000Hz, 16 bits per sample, mono.

DSD and mbelib should compile on Linux and *BSD operating systems. Any linux
distribution should work as long as it has support for your audio devices.
DSD version 1.3 and later requires mbelib 1.2 or later.

Copyright License

DSD and mbelib are both released under a BSD style copyright license. This means that
as far as copyrights are concerned it can be freely copied and used, including for commercial products as long as the original copyright notice is included. (however see important patent issues section below)

Patent Issues with mbelib

While DSD was intended to be patent-free, mbelib describes functions that
may be covered by one or more U.S. patents owned by DVSI Inc. The source code itself should
not be infringing as it merely describes possible methods of implementation.
Compiling or using mbelib may infringe on patents rights and/or require licensing.
It is unknown if DVSI will sell licenses for software that uses mbelib. If you do
not have a license and are in a jurisdiction protected by the DVSI patents you should
not compile or use this source code.

A: No, because OS X does not use the traditional unix-like /dev/audio interface. It should
be easy for someone familiar with mac audio programming to port it to the Mac.

Q: Will you support decryption if I lawfully posess the encryption keys?

A: From the README file:

Decryption of speech is NOT supported, even if you lawfully posess the
encryption keys. Decryption support will not be added in the future as
the authors wish to steer as far away from the legal issues associated
with encryption as possible.

Q: Who are the author(s)?'

A: The author(s) are anonymous but PGP keys are provided inside the packages
so future releases/communications can be verified.